How the brain signals to the immune system during systemic inflammation is not known. Mice were engineered to express a reporter gene exclusively in haematopoietic cells (immune precursors). This reporter was found to be secreted by haematopoietic cells in the form of exosomes and taken up and expressed by Purkinje neurons. Purkinje cells that had taken up the mRNA-containing exosomes showed differences in microRNA profiles, suggesting that signalling between haematopoietic cells and Purkinje neurons has physiological consequences and might play a part in neuroimmune signalling during chronic inflammation.